The feasibility of competitive replacement of potentially harmful fatty acids associated with certain neurological diseases with a common fatty acid was successfully tested in vitro and in vivo; in the latter case, by dietary supplementation. The abnormally elevated serum concentration of hexacosansate in adrenoleukodystrophy was substantially decreased following long term feeding with triolein. This phenomenon could be useful in treatment of these patients. In a continuing work on Lambda5 and Lambda6 fatty acid reductases in human fibroblasts no decline was observed in these enyzmatic activities with increasing passage number of cultures and cell senescence.